As a disk apparatus, for example, a magnetic disk apparatus includes a magnetic disk arranged in a case, a spindle motor for supporting and rotating the magnetic disk, a magnetic head for reading/writing information from and to the magnetic disk, and a carriage assembly for movably supporting the magnetic head to the magnetic disk. A head section of the magnetic head includes a recording head for writing and a read head for reading.
Recently, a recording head making use of perpendicular magnetic recording has been proposed to increase recording density and the capacity of a magnetic disk device or to reduce the size of the magnetic disk device. In the magnetic head, the recording head has a main magnetic pole for producing a perpendicular magnetic field, a trailing shield opposed to a trailing side of the main magnetic pole with a write gap therebetween, and a coil for directing magnetic flux to the main magnetic pole.
To improve the recording density, there has been proposed a magnetic head employing a high-frequency magnetic field assist record system that includes a spin torque oscillator as a high-frequency oscillator interposed between a main magnetic pole and a trailing shield and applies a high-frequency magnetic field from the spin torque oscillator to a magnetic recording layer. It becomes possible to produce a large high-frequency magnetic field and to realize stable read/write characteristics by supplying a drive current to the high-frequency oscillator and oscillating a magnetization of an oscillation layer in a sufficient amount of amplitude.
The spin torque oscillator employs a spin injection layer having a coercive force smaller than a magnetic field applied from the main magnetic pole. With the configuration, since the direction of a recording magnetic field and the magnetization direction of the spin injection layer become the same at all times, stable oscillation can be obtained. However, in the spin torque oscillator constructed as described above, there is a problem in that the spin torque oscillator cannot employ a spin injection layer having a coercive force larger than a magnetic field applied from a main magnetic pole.
Further, magnetization reversal of the spin injection layer is executed by a gap magnetic field of a write head. Accordingly, even if a magnetization reversal speed of the spin injection layer is increased, the magnetization reversal of the spin injection layer inevitably occurs with a time lag from a reversal of the gap magnetic field, with a result that it is difficult to improve speed responsiveness of the magnetization reversal.